Level 1: Blow up building near sub terranian peice with your missiles and lasers. You'll get laser level 2 and your missiles back.
Level 2: Use the Doomsday monster's tale as a weapon.
Level 3: Destroy the main monster before returning to the mission.
Level 4: Underneath all of the construction hides an extra life.
Level 5: Power 4 blasters are underneath the reactor core. You must already have Powers 2-3.
Level 6: There's a secret weapon underneath the guardian.
Level 7: Use missiles to defeat the jumpers + spiders.
Level 8: Get the mirror lazer beforehand and save up fuel - you'll need it.
Level 9: Kill the spike-jumper and a secret compartment opens up. Inside is an extra life.